A strange thing happens to nearly everybody at night. They turn off the lights, put up the covers and close their eyes. Six or seven hours later, they wake up again. Strange, isn’t it?
Sleep puzzles science. Scientists and doctors would rather talk about why one can’t fall asleep. They are not so sure what causes sleep.
The best conditions for sleep, they say, are good health and meal neither too big nor too small. No worries and a comfortable place to sleep in are important, too. They advise against two in one bed.
Strange things happen during sleep. For example, you move often. You would feel tired if you didn’t. You also dream. Part of your brain is still awake when you dream. Dreaming happens when the memory and imagination parts of your brain are still awake. Experiments have shown that bad dreams may be caused by a stomachache.
Don’t worry if you dream. Some great stories and poems were begun while the writers slept.
41. Sleep puzzles scientists because they are not certain _______. 
why one can’t fall asleep
why one wakes up six or seven sleeping hours later
both A and B
D. what causes sleep
42. You would feel tired during sleep if you ________.
A. move often           B. sleep on your back     C. didn’t move    D. went back too later
43. Dreaming happens when _______.
A. you are in a deep sleep                           B. you are not comfortable
C. part of our brain is still awake               D. there’s too much noise  in the room
44. The best title for this passage is ________.
A. Why You Dream                              B. The Strangeness of Sleep
C. What Happens During Sleep            D. The Cause of Sleep    

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